On rotating a point charge having a charge \(q\) around a charge \(Q\) in a circle of radius \(r\), the work done will be:

1.	\(q \times2 \pi r\)	2.	\(q \times2 \pi Q \over r\)
3.	zero	4.	\(Q \over 2\varepsilon_0r\)

If a charged spherical conductor of radius 10 cm has potential V at a point distant 5 cm from its centre, then the potential at a point distant 15 cm from the centre will be -

(1) $\frac{1}{3}V$

(2) $\frac{2}{3}V$

(3) $\frac{3}{2}V$

(4) 3 V

The ratio of momenta of an electron and an $\alpha$-particle which are accelerated from rest by a potential difference of 100 volt is 

(1) 1

(2) $\sqrt{\frac{2m_e}{m_{\alpha }}}$

(3) $\sqrt{\frac{m_e}{m_{\alpha }}}$

(4) $\sqrt{\frac{m_e}{2m_{\alpha }}}$

Ten electrons are equally spaced and fixed around a circle of radius R. Relative to V = 0 at infinity, the electrostatic potential V and the electric field E at the centre C are:

A proton is about 1840 times heavier than an electron. When it is accelerated by a potential difference of 1 kV, its kinetic energy will be -

(1) 1840 keV

(2) 1/1840 keV

(3) 1 keV

(4) 920 keV

As per this diagram a point charge +q is placed at the origin O. Work done in taking another point charge –Q from the point A [co-ordinates (0, a)] to another point B [co-ordinates (a, 0)] along the straight path AB is

(1) Zero

(2) $\left(\frac{{\displaystyle -qQ}}{{\displaystyle 4\pi {\epsilon }_0}}\frac{{\displaystyle 1}}{{\displaystyle a^2}}\right)\sqrt{2}a$

(3) $\left(\frac{{\displaystyle qQ}}{{\displaystyle 4\pi {\epsilon }_0}}\frac{{\displaystyle 1}}{{\displaystyle a^2}}\right)\frac{a}{\sqrt{2}}$

(4) $\left(\frac{{\displaystyle qQ}}{{\displaystyle 4\pi {\epsilon }_0}}\frac{{\displaystyle 1}}{{\displaystyle a^2}}\right)\sqrt{2}a$

The capacity of a condenser is 4 × 10^–6 farad and its potential is 100 volts. The energy released on discharging it fully will be -

(1) 0.02 Joule

(2) 0.04 Joule

(3) 0.025 Joule

(4) 0.05 Joule

The energy stored in a condenser of capacity C which has been raised to a potential V is given by -

(1) $\frac{1}{2}CV$

(2) $\frac{1}{2}C{V}^2$

(3) CV

(4) $\frac{1}{2VC}$

Eight drops of mercury of equal radii possessing equal charges combine to form a big drop. Then the capacitance of bigger drop compared to each individual small drop is 

(1) 8 times

(2) 4 times

(3) 2 times

(4) 32 times

The capacity of a parallel plate condenser is C. It's capacity when the separation between the plates is halved will be?

(1) 4 C

(2) 2 C

(3) $\frac{C}{2}$

(4) $\frac{C}{4}$